Why is our toilet drain pipe so incredibly loud?
October 26, 2012 1:20 PM   Subscribe

Plumbing filter: Why is there an incredibly loud noise on the first floor when the second floor toilet is flushed, and can this be fixed?

Our house was built in 1999. If you are in the guest room downstairs and someone flushes the upstairs toilet, there is a *very* loud sound of water rushing behind the guest room wall. It's like standing next to a thundering waterfall - this isn't like a faint sound of hearing a flush in a distant room or water trickling in a pipe. Obviously the drain pipe from the toilet must go through this wall, but I have lived in other 2-story houses before where this was not an issue. It is not ideal to have guests staying in the guest room and worry about waking them up via toilet flush from the 2nd floor (it really is abnormally, alarmingly loud). I haven't seen evidence of water leakage so it seems like it's not so much that something is broken, but rather was poorly implemented to begin with.

Can this be fixed by replacing the drain pipe with something quieter? Insulating it somehow? It wouldn't surprise me if the issue came down to the builders using cheap materials in the first place; we have already found instances where ducts from the HVAC system open up into cabinets (instead of vents) and it generally seems like the developers cut corners during construction.
posted by Mallenroh to Home & Garden (13 answers total)
Is the flush exceptionally strong? We had several of these toilets in our last house! This is generally seen when your septic tank is far away from the house, or other weird little reasons, like having a basement toilet that needs to pump upwards. We were never able to quiet it :( I think rather than cheap materials, this is because the system has been designed to be STRONG.
posted by MangyCarface at 1:24 PM on October 26, 2012 [1 favorite]

Older homes often used cast iron stacks encased in plaster walls; newer homes basically use thin wall PVC behind uninsulated drywall. I'm not sure it's the builder's fault; more the architect's fault for putting the stack in a bedroom wall rather than a dedicated and insulated utility chimney.
posted by seanmpuckett at 1:49 PM on October 26, 2012

They likely used ABS instead of cast iron waste lines. You can theoretically upgrade to cast iron, or you can add additional acoustical insulation (e.g. fiberglass batts), or you could even double up the drywall on that wall to add mass, which is another effective acoustical barrier (see also: cast iron).

(on preview, okay, I will attempt to defend my profession by saying that the reference to "developers" in the question almost guarantees that no architect was involved in the design)


posted by misterbrandt at 1:53 PM on October 26, 2012 [3 favorites]

It shouldn't be that noisy. I'd start considering that the air displaced by the flush is not being vented properly. All that noise is probably the downward water meeting air that has no place to go.

A house built in '99 in the States would typically have a small roof vent for each bathroom. Maybe you should snake those, or maybe that was another corner cut by the builder. Or maybe the people for whom the house was built changed the floor plan a few times during later stages of construction.
posted by Mr. Yuck at 2:05 PM on October 26, 2012 [1 favorite]

I was thinking that you might put Padded Wall Panels on the wall where the stack is that the sound might be muffled considerably.

You can probably do this with some plywood, a stable gun, some foam padding and attractive/cheap fabric (Ikea is a good source).
posted by Ruthless Bunny at 2:06 PM on October 26, 2012

for various reasons the drain pipe for my toilet (PVC thank you very much) goes uncovered down my dining room wall. the sound of water flushed through the pipe is fairly loud and it's not the drain vent. modern toilets flush at higher velocities than older ones, plus PVC or ABS is much lighter than cast iron and thus not as quiet.

What you are looking at is tearing out the sheetrock in the guestroom where the drain runs and sound insulating the pipe, because I bet they either didn't sound dampen the drain pipe or did a totally half-assed job of it. the real problem is that the builders put a guest room under the bathroom, but not much you can do about that now. this insulation is usually done in older houses with fiberglass batting, but I bet you could do better with polyurethane foam aka sprayfoam if you were willing to experiment. then, since you;ve already torn out the sheetrock you could double up the sheetrock on that wall when you replace it.

or use chamber pots when you have guests...
posted by ennui.bz at 2:41 PM on October 26, 2012

If you have guests infrequently, could you just use the downstairs bathroom at night? Otherwise, you're looking at ripping out walls and whatnot.
posted by zug at 2:47 PM on October 26, 2012

I ripped out the wall and insulated it with soundproofing. Otherwise anyone downstairs was woken up by the toilet or shower upstairs. It was a few hundred bucks and totally worth it.
posted by fshgrl at 3:30 PM on October 26, 2012

Nthing that this is a problem with a lack of sound deadening material.

One easy fix that will attenuate the sound a bit would be to drill a hole at the top of the wall and then pour in either a foam or cellulose insulation. Such insulation lack mass so won't completely kill the noise but they will muffle it somewhat and they attenuate much of the high frequency noise.

Mr. Yuck writes "A house built in '99 in the States would typically have a small roof vent for each bathroom. Maybe you should snake those, or maybe that was another corner cut by the builder."

YMMV, best practice around here is to interconnect all the vents into a single pipe that then penetrates the roof. This both looks better and reduces the number of penetrations (which are often where leaks develop).
posted by Mitheral at 4:16 PM on October 26, 2012 [1 favorite]

Seconding the vent pipe.

Is running the waste pipe down outside the wall an option, or otherwise re-routing it?
posted by GeeEmm at 10:18 PM on October 26, 2012

I doubt it's the vent pipe. Lacking one would cause gurgling and burping noises in the bathroom using the water, not further down. The waterfall sound is water flowing unimpeded through PVC pipe in uninsulated walls.
posted by gjc at 12:05 AM on October 27, 2012

There might be some unfortunate geometry where, rather than running down the walls of the pipe, the waste free falls for a considerable distance before hitting a hard bend (literally like a waterfall). If the pipe isn't strapped down in the right places, it'll act like a big cylindrical resonating chamber (the way the body of a guitar amplifies the vibration of a string). A bit of padding (and maybe a couple more straps) around the pipe will probably dampen it a huge amount.

I had a similar situation with a downspout that always woke up the neighbours.
posted by bonobothegreat at 1:18 PM on October 27, 2012

IMHO, if the very loud sound is something resembling an amplified "glug glug glug" [occurring especially toward the end of the flush] then it is likely to be a venting problem. We had something similar in our bathroom, and we fixed it by inserting a small ball vent under the bathtub that was connected to the same drainage line.
posted by rudster at 1:21 PM on October 28, 2012

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